2.) RAW photos need to be edited on a computer afterwards and give the best possible quality if this is done. Jpeg gives better quality if no editing is done. I guess RAW + L is for those who dont know if they are going to edit yet (and for those with a large hard drive!)

1,I know that lowering your ISO makes your picture darker, but does it also improve the image quality?

Well that's not exactly true, unless you are set to Manual mode with a fixed shutter and aperture setting - then you will notice the photo getting darker as ISO goes down, or brighter as it goes up. The reality is that ISO is one of the three primary tools used to accomplish exposure, along with shutter and aperture. Lowering the ISO reduces the 'gain' of the sensor, meaning in order to get more brightness, you need to get more light to the sensor - by either using a slower shutter speed or a bigger aperture. Like anything when the 'gain' is turned up, things get noisier or grainier (ever deal with old HAM, CB, or shortwave radios and turn up the 'squelch' or gain knob? - more static noise but more sensitivity to fainter signals. ISO works the same way). In general, most photographers agree that the best approach to ISO is to use the lowest ISO you can to still get the shot you need. Manipulate shutter speed to be as fast as you need it to be, or aperture as open or closed as you need for depth of field...only if those two can't be optimally set do you then go to ISO to boost it up until the other two parameters are where you want them. The short answer to part 2 of your first question is...yes - lower ISO delivers much better quality, with greater detail, color fideltiy, and lower noise.

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2, I normally take pictures that come out as JPEG pics (large 18MP 5184x3465), but what about RAW pictures? When are you supposed to take pictures using RAW + L? and why?

This always opens up a floodgate in camera forums. The problem is that there tend to be three very distinct groups of thought:

1. RAW is the ONLY way to shoot, you are not a professional unless you do, you are only 1/2 a photographer, you're a bit daft too, clearly ignorant, blind, and a bit stupid, and will never realize how poor of a photographer you are until you learn to shoot and process RAW.

2. JPG is the ONLY way to shoot, RAW is a waste of space, waste of time, only for lame photographers who can't get it right in camera so they have to make up for it with processing, RAW supporters are egotistical judgmental fools, techheads who prefer time spent in front of a computer creating their photos than out taking them.

3. (and this group is very small, usually lost in the argument of the above two groups) - Both JPG and RAW are optional ways of shooting, both with their own positives and negatives, and each person needs to decide for themselves what format is best for their needs, their time, their photography, and their results. Also, very fine photographers can get excellent results from both formats, a photographer who gets things right in camera and knows how to set up their camera will do better in either format than someone who doesn't, and accepting that JPG has advantages in convenience and space and RAW has advantages in editing latitude and processing flexibility.

It's more than likely that you are going to hear from one of the first two groups who is going to try to convince you that despite all of this, you really should be shooting in * (RAW/JPG) because you * (are better off learning how to control and shoot with the camera and not relying on the computer to fix your problems/will never be a proper or professional photographer or realize your potential if you let the camera make the image for you).

Hmm - yes and no. Keeping ISO lower will result in cleaner images with less digital noise, and depending on your camera you will learn what the threshold is for levels of noise that you are happy with.

Some DSLRs will let you go below your base ISO. For example, on my Nikon D90 the standard base ISO is 200, but I can push this to ISO100 if required. I use the when I want to push shutter speeds slower for effect with filters.

However this can reduce image quality a little compared to ISO200, as there can be less contrast depending on the scene.

I'm in zackiedawg's group 3, shooting RAW + JPG. Generally I'm shooting in RAW + JPG basic as this gives me thumbnails when reviewing shots on the computer. You will find people answering this question in several ways depending on their requirements.

Generally, extremely high ISOs (Such as 3200 or 6400) and lower ISOs (Like anything 100 or lower) will degrade the image quality, so I'd only use them when necessary. For example, a few days ago I was taking pictures of fish in my aquarium. I needed to use a macro lens and an extension tube (Which I believe made the lens about f/7) in poor lighting. I needed an ISO of 6400 to get shutter speeds that couldn't blur the image, but of course they were relatively noisy as well. Low ISOs like 100 won't degrade the IQ as much as an extremely high ISO (They change the image quality in different ways), but it will still have an effect.

Shooting RAW won't throw away any information about the image, the IQ is higher, the file isn't compressed and it's great to post process RAW files. However, they use a lot of space on your hard drive and they can't be opened with most programs. I usually only shoot RAW for my astrophotography, as I usually post process it. Otherwise, I'll shoot JPEG.

I generally stick to ISO200 as there can be a reduction in contrast. Contrast is lacking where I live, so I need every bit that I can get. There's no improvement in noise (obviously pretty low at 200 anyway)

I drop to ISO100 if I'm using filters and need to push things further to get an extra stop of shutter speed.

You've got a few approaches - the first is that RAW will usually look considerably LESS sharp than JPGS initially, since they haven't been processed yet...the camera is applying whatever level of JPG sharpening you've set it to - so the amount of JPG sharpening you are seeing is variable.

Have you tried adjusting the sharpness level in the camera for your JPGs? This could be a contributing factor.

Also note: even most JPG shooters will apply some sharpening when post processing a photo - compressed or not, shooting JPG doesn't mean you cannot sharpen, and in fact sharpening is one of the easier types of processing to apply to a JPG - it's when you get into pulling shadows or highlights or altering colors and white balance drastically that RAW will have the bigger advantage. Most of the time, you'd want to use sharpening tools like USM (Unsharp mask) or High-pass, rather than using the 'sharpen' tool.

Note too that sharpness is heavily dependent on lens and aperture choice. You can shoot JPG or RAW, but if you've got a soft lens, you're getting soft results. You can try to spiff them up in processing, but it will never equal a truly sharp lens. Also, some lenses can be extremely sharp when stopped down a bit - shoot with the largest aperture, and the lens could be considerably soft wide open...and on the other end of the spectrum, shoot with the aperture stopped down too much and you lose sharpness to diffraction. Make sure the lens you are using is optimally sharp, know its 'sweet spot' aperture, and you shouldn't really need too much or any post-processing sharpening, and JPG vs RAW will have little major discernable difference (sharpness-wise).

Absolutely - that's true moreso of cheaper lenses, but basically true of all - wide open or fully stopped down apertures are almost never a lens' best image, nor are the most wide angle or longest telephoto of most zooms. There are sometimes exceptions, but most of the exceptions have a price to match their exceptionalism.